In wireless transmission procedures, including the delivery of MBS, it is necessary to reference a particular MAC (Media Access Control) frame. For instance, a BS (Base Station) may signal to an UE (User Equipment) in what frame it expects to receive a particular message, or in what frame it must send a particular message, or in what frame it must invoke a particular behavior. Currently, in 802.16 (and LTE) networks, two methods are used for referencing a frame. In the first method, the BS includes in its message an absolute frame number to refer to a frame where the specific activity needs to take place. In the second method, the desired frame is indicated by the BS using a frame offset with respect to the current frame.
Using absolute frame numbers has shortcoming. For example, conventional base stations in a network may not synchronize their frame numbering. That is, when one BS transmits a frame numbered M1, a neighboring BS may be transmitting a frame numbered M2. Therefore, absolute frame numbers can only be used when the BS with respect to which the reference is given is known to the UE (a fixed, nomadic or mobile station). This is not always the case. Some examples include the following: (1) when the UE exits Idle Mode; (2) when the UE is listening to pages or broadcast announcements; and (3) when the UE is receiving an allocation at a target BS and there are several potential target BSs (as is the case in, for example, macro-diversity reception from multiple BSs).
Use of the frame offset method also has short comings. For example, the message that contains the frame offset needs to be received in a particular frame. This imposes constraints on the BS scheduler, which needs to ensure that the message is transmitted and received in a particular frame, as delaying transmission would result in the offset information being invalid. Furthermore, if the message is fragmented, or if the message requires multiple HARQ or ARQ retransmissions, the receiver must be able to determine when the first fragment or HARQ/ARQ transmission occurred, which complicates the implementation of the receiver.
Current wireless systems also incorporate modes to deliver Multicast and Broadcast Services (MBS) data. For example, IEEE802.16 and LTE support MBS (LTE uses the term MBMS (Multimedia Broadcast/Multicast Service)). A shortcoming of present schemes is that to achieve PER (Packet Error Rates) that are required for broadcast or multicast video and audio applications and data-casting, a wireless network must typically use overly robust and inefficient MCS (Modulation and Coding Schemes) or must somehow employ a retransmission scheme more suited to file transfer than for real time consumption of a Multicast or Broadcast Service.